Lifeline : STARGATE ATLANTIS SEASON FOUR ....

ANALYSIS

Atlantis has a new, Asuran-constructed Zero Point Module to power the city, which replaces the nearly-depleted Z.P.M. used to flee the planet Lantia and keep the city alive in deep space. That original power unit is probably not quite fully depleted yet, but even with the new Z.P.M. the city does not have an abundance of power.Thanks to a bit of hacking from Rodney McKay, the team has managed to reactive the core command in the Replicators' base code: to attack the Wraith relentlessly, as the Ancients originally created them to do ("Progeny"). Once the revised code was sent to the entire Asuran population during a collective update, they immediately launched a fleet of ships headed for a Wraith planet.

The Replicators and the Wraith are going to war.
It is not known, however, just why this command had been deactivated to begin with. It may explain why the Asurans claimed to have a plan to deal with the Wraith at a time of their choosing ("Progeny") -- but had gone at least 10,000 years beyond the Ancient-Wraith war without acting.
It has been established, however, that the Asurans are incapable of altering their own base code ("Progeny"); thus Niam needed McKay to alter the part of their base code that made them fundamentally aggressive, in the hopes that doing so would allow them to ascend.
It may be, then, that the Ancients themselves deactivated the imperative to attack the Wraith, for reasons that remain a mystery. In that case, reactivating it may have unforeseen consequences.
It is also not outside the realm of possibility that the Wraith themselves found a way to alter the Replicators' base code, to take them out of their fight against the Ancients thousands of years ago. This stratagem may have proved a significant turning point in that conflict.
The city of Atlantis has a new home, having fled its original planet, Lantia, to escape the Replicator satellite weapon. The surface of the planet is mostly covered by ocean, though there are some land masses with indigenous plant and animal life (including a venomous snake). The planet has five moons.
The city's new home planet is apparently also closer to Asuras, the Replicator homeworld. It is now within range of Atlantis's long-range sensors, allowing them to monitor activity such as the launch of Replicator warships. This is, of course, also a potential disadvantage to Atlantis should the Replicators ever discover where Atlantis is. Their own long-range sensors should be at least as powerful as Atlantis's sensors.
Elizabeth Weir is still alive, having been healed from her injuries by the Replicator nanites that are now keeping her alive. These nanites also allow her to access the Replicators' collective, enabling her access to information and a measure of control over them. But she has been captured by the Replicators, and it is not clear just what they will do with her -- if they will kill her, interrogate her, or try and convert her and use her to their own ends.
The loss of Weir into the hands of the enemy is, at the very least, a major security breach for Atlantis and for Earth. Even though she does not know the location of Atlantis's new home, even though passwords can be changed, the Replicators conceivably now have access to everything she knew: Earth and the Milky Way Galaxy, the Milky Way Replicators, planets visited by the team and other races encountered, Earth's battle cruisers, the Midway Space Station, technological and tactical information, the anti-Replicator weapon and plans for a planet-wide version capable of wiping out a planet of Replicators, etc.
With Elizabeth Weir lost, who will be assigned command of the Atlantis expedition? As the next most senior member (and the senior military officer on the base), temporary leadership falls to John Sheppard. But it no doubt won't be long before the International Oversight Advisory assigns a replacement for Weir. Whether or not that person is military or civilian, and from the United States or a different I.O.A. member nation, may have a significant impact on the future of the expedition.